When you really understand and accept this, it's incredibly liberating.
No matter how much you plan, how many meetings you call, or how much research you do, you'll never think of everything. Instead of trying to get it perfect the first time, move early and make sure you have tight feedback loops to evaluate how you're doing and make improvements.
This is true for product development. It's true for building basically anything of any complexity. It's definitely true for building routines and procedures for your team.
How do you improve those routines? Listen to your developers. They're the ones who are using them every day to get their jobs done, and they'll have strong opinions about what's working and what's not. Is their purpose unclear? Are they onerous to follow? Make space for your team to discuss them openly and to present new ideas. Developers are problem solvers, remember?